Oxfam's former head of operations in Haiti has admitted to having a sexual relationship with a woman he helped in the aftermath of 2010's earthquake, but denied paying for sex with prostitutes or abusing minors.

Oxfam's former head of operations in Haiti has admitted to having a sexual relationship with a woman he helped in the aftermath of 2010's earthquake, but denied paying for sex with prostitutes or abusing minors.

Roland van Hauwermeiren defended his behaviour during overseas aid work between 2004 and 2011 in an open letter.

One of the world's best-known and biggest disaster relief charities, Oxfam has been under fire since reports emerged that some of its staff paid for sex with prostitutes after a devastating earthquake hit the Caribbean island.

It has neither confirmed nor denied that specific account, but has said an internal investigation in 2011 confirmed sexual misconduct occurred, and it has apologised.

Mr van Hauwermeiren said he never used prostitutes while co-ordinating the crisis relief effort in the Caribbean country. But he said he was "deeply ashamed" by aspects of his behaviour.

On his work in Haiti, he said: "Myself, indeed, I am not perfect, I am not a saint - a man of flesh and blood, and have made mistakes (not easy to admit), and I am deeply ashamed. I indeed admitted to investigators that I had three times intimate contact in my house.

"It was, in my opinion, a mature honourable lady, not an earthquake victim and no prostitute, whom I had met since I supported her young sister and very young mother with diapers and powdered milk. I never gave them money.

"I also had frequent visits from a language prof (a lady), my driver, the younger brother, sisters and grandmother of the young lady in question.

"There were also frequent attempts by ladies and gentlemen to enter my house with all sorts of excuses to ask for money, to offer a job on the demands or sexual services. (Should I have lied ????). I never accepted those advances.

"I have never visited in a brothel, nightclub or bar in the city or this country."

Two members of staff were fired for luring prostitutes to their room during a house party, he said, but the men insisted the women had freely offered themselves.

He claimed his dismissal of the pair earned the nickname "terminator" because of his decisive action.

The letter continued: "I offered my resignation for the following reasons:

"1. I should indeed have acted harder and faster when the rumours had spread. I found and still find this a lack in my leadership,

"2. Through my relationship with the lady I fed the rumors that I was also involved in such scandals (ie the parties or prostitution visit). As director I should have given the example and I had compromised the organisation and myself.

"3. I had already been in dispute with Oxfam for technical matters before and the facts above made up the barrel."

His letter concluded with a condemnation of sex parties with prostitutes as "reprehensible" and stating his support for offenders to be punished, but expressed concern the crisis with Oxfam could now threaten its work.